1. Technical Field
The present disclosure relates to metal materials suitable for magnetostrictive actuators and sensors. More particularly, the present disclosure provides iron/gallium (Fe—Ga) sheet materials with a textured surface and a process for texturing the sheet materials.
2. Background of Related Art
Iron/gallium (Fe—Ga) alloys are known as a magnetostrictive alloy composition called Galfenol. Magnetostrictive materials are broadly defined as materials that undergo a change in shape due to change in the magnetization state of the material. Nearly all ferromagnetic materials exhibit a change in shape resulting from magnetization change. In materials such as iron, the change in length is on the order of 10 parts per million (ppm). Such shape changes of 10 ppm or less are not very useful.
Alloys which exhibit magnetostrictive properties such as greater than 50 ppm can be problematic in that the magnetostrictive properties are generally obtainable by providing very large magnetic fields such as greater than 1000 oersteds, or extremely low temperatures such as below 50° C., or both. Having to provide a large magnetic field, or hold an alloy at low temperatures in order to change the shape of the alloy is undesirable and unacceptable for many engineering purposes. Thus, materials capable of magnetostrictive strains (A) on the order of 100 ppm or greater with low saturation fields of less than several hundred oersteds with limited temperature dependence are desirable.
Attempts have been made to solve these problems by using alloys incorporating rare earth materials, such as Terfenol-D, a specially formulated alloy of terbium, dysprosium, and iron that exhibits magnetostriction at room temperature and relatively small applied fields. Terfenol-D overcomes the temperature problem by incorporating a RFe2 microstructure which raised the curie temperature above room temperature. The necessary magnetic field was reduced by balancing the ratio of terbium and dysprosium. However, Terfenol-D is not suitable for all engineering purposes and it may crack when subjected to certain stresses such as being made into a sheet. Moreover, there is a significant cost in manufacturing the material.
Although iron/gallium (Fe—Ga) alloys are magnetostrictive, known polycrystalline iron/gallium compositions have not been very useful because they are brittle and susceptible to cracking when shaped into a sheet. For example, when iron/gallium alloy is subjected to hot rolling at 1000° C., it forms brittle sheets that fracture under low stress conditions. Accordingly, thin sheets which are desirable for use at higher frequencies are problematic to form. Thus, there remains room for improvement in formulating polycrystalline Fe—Ga compositions, and especially to provide Fe—Ga alloy compositions having: large saturation magnetostriction potential in low applied fields; excellent mechanical strength; excellent ductility; and excellent sheet formation characteristics when compared to state-of-the-art alloys.